1. Field of the Invention
The present invention relates to a substrate processing method and a substrate processing apparatus for forming a thin film on the surface of a substrate, e.g., a semiconductor wafer, etching the thin film formed on the surface of the substrate and etching the surface of the substrate.
2. Description of the Related Art
As is known well, several methods are available for forming a thin film on the surface of a substrate, e.g., a semiconductor wafer. Vapor-phase growth is one of those methods. Vapor-phase growth utilizes chemical reaction of a source gas at a high temperature, and is advantageous in that, e.g., various types of films can be obtained with a high adhesion strength and film thickness control is comparatively easy. As a substrate processing apparatus for actually forming a thin film on the surface of a substrate, a batch type apparatus that forms films on the surfaces of a plurality of substrates simultaneously is widely used.
In recent years, however, due to an increase in diameter of the semiconductor wafer as the substrate, it is difficult to maintain the film formation uniformity within the surface of the wafer or between wafers with the batch type apparatus. From this reason, in the field of semiconductor element manufacture, a single wafer processing apparatus that forms films on the semiconductor wafers one by one is used more often.
In the single wafer processing apparatus, the film formation rate must be increased to increase the throughput. In order to increase the film formation rate, it is proposed to form a film with an increased film formation temperature while rotating the substrate. More specifically, when the substrate is rotated, the gas in the vicinity of the surface of the substrate can be moved with the centrifugal force, thereby decreasing the thickness of the boundary layer. As a result, the source gas can be easily diffused toward the high-temperature substrate, so that the film formation rate is increased. This operation is effective when etching the thin film formed on the surface of the substrate as well. More specifically, since the diffusion rate of the etching gas toward the high-temperature substrate can be increased, the time required for etching can and the diffusion rate of the product gas from the high temperature substrate be shortened.
In the substrate processing apparatus that rotates the substrate during film formation or etching as described above, a substrate holder arranged in a processing vessel must be rotatably supported by some means, and a rotational drive force must be supplied to this supporting means. The most general way to realize this is to directly couple a rotating shaft to the substrate holder, to support the rotating shaft with a bearing, e.g., a ball bearing, and to supply a rotational force to the rotating shaft from a motor.
In the substrate processing apparatus that rotates the substrate during film formation or etching, the substrate must be held at a high temperature, e.g., 300.degree. to 1,200.degree. C., as described above. Then, heat is transferred from the substrate holder to the bearing or motor through the rotating shaft, thus heating the bearing and motor to a high temperature.
When heat is transferred to the bearing, the temperature of the inner ring becomes higher than that of the outer ring, and the balls present between the inner and outer rings are strongly pushed by the two rings due to the difference in thermal expansion accompanying the difference in temperature. As a result, rotation of the rotating shaft becomes unstable to form non-uniformities in the formed films. In the worst case, it becomes difficult for the substrate holder to hold the substrate and the substrate is thus disengaged from the substrate holder. The bearing and motor use a lubricating oil, a resin material, and the like that normally start to be decomposed when their temperature exceeds 200.degree. C. For example, in the use of even a fonbrin-based lubricating oil having a low vapor pressure, when the temperature exceeds 200.degree. C. the vapor pressure is largely increased. The decomposition products of the lubricating oil, the resin material, and the like largely contaminate the target substrate and, for example, degrades the film quality in film formation.
When the lubricating oil, the resin material, and the like are decomposed along with an increase in temperature, the lubricating oil becomes short or electrical insulation becomes insufficient. Then, a rotational drive mechanism including the bearing is greatly damaged in this regard as well.
In order to eliminate the inconveniences described above, normally, the length of the portion of the rotating shaft from the substrate holder through the bearing is sufficiently increased, so that heat will not be easily transferred to the rotational drive mechanism including the bearing. Then, however, the rotating shaft is supported almost in a cantilever manner. This makes it difficult to obtain stable rotation and increases the number of times of maintenance, leading to a low throughput.
As described above, in the substrate processing apparatus that rotates the substrate during film formation or etching, the target substrate must be held at a high temperature of 300.degree. to 1,200.degree. C. during processing. Thus, heat is transferred from the substrate holder to the rotational drive mechanism including the bearing through the rotating shaft. This heat may cause an erroneous operation of the rotational drive mechanism, or the formed film may be contaminated with the gas generated by the rotational drive mechanism. When the length of the portion of the rotating shaft from the substrate holder through the bearing is sufficiently increased in order to solve this problem, it becomes difficult to obtain stable rotation, the number of times of maintenance is increased, and the throughput cannot be increased.
It is an object of the present invention to provide a substrate processing method and a substrate processing apparatus that can suppress transfer of heat from a substrate holder to a rotational drive mechanism including a bearing through a rotating shaft, thereby preventing occurrence of inconveniences as described above.